Rotavirus can now br grown readily in cell cultures by techniques originally described by Japanese investigators which include pre-treatment of virus with trypsin, incorporation of trypsin in the maintenance medium, and incubation of roller tube cultures on a roller apparatus. Our objectives in this project are three-fold: (1) to cultivate directly in cell cultures a variety of human and animal rotavirus strains derived from diverse geographical areas and populations; (2) to define serotypic diversity and similarity among these viruses based on their VP4 and VP7 specificities; and (3) to select and develop potential rotavirus vaccine candidates (including direct cell-culture isolates or laboratory produced reassortant strains). In this project, the serotype of rotavirus isolates was characterized by plaque-reduction neutralization (PRN) assay. Three single VP7 gene substitution reassortants were generated using a porcine rotavirus Gottfried strain (VP7 serotype 4) and human rotavirus strains D (VP7 serotype 1), DS-1 (VP7 serotype 2), or M (VP7 serotype 3), each of which possesses only the VP7 gene of D, DS-1, or M with the remaining ten genes being derived from the Gottfried strain. Hyperimmune guinea pig antiserum raised against the reassortant strain Gottfried x DS-1, neutralized not only the parental strains Gottfried and DS-1 but also human rotaviruses belonging to VP7 serotype 1 (Wa strain), 3 (P strain), or 4 (VA70 and ST3 strains).